Thermodynamic analysis of the tetragonal to monoclinic transformation in a constrained zirconia microcrystal: Part 2 In the presence of an applied stress

A thermodynamic analysis was made of a simple model comprising a transforming t-ZrO sub(2) microcrystal of size d constrained in a matrix subjected to a hydrostatic tensile stress field. The field generated a critical size range such that a t-particle transformed if d sub(cl) < d < d sub(cu). The lower limit d sub(cl) exists because at this point the maximum energy (supplied by the applied stress) which can be taken up by the crystal is insufficient to drive the transformation. The upper limit d sub(cu) is a consequence of the microcrystal being so large that it transforms spontaneously when the material is cooled to room temperature. Using the thermodynamic (Griffith) approach and assuming that transformation toughening is due to the dilational strain energy, this mechanism accounted for about one-third of the total observed effective surface energy in a pak-aged Ca-PSZ alloy.